What does the shaft turning gear (also known as jacking gear) achieve in maintenance?

The shaft turning gear, or jacking gear, is an essential component during maintenance activities on a ship's propulsion system. Its primary function is to facilitate the manual rotation of the ship's propeller shaft when the main engines are not running. This capability is critically important for several reasons, primarily to prevent warping of the shaft and to ensure proper alignment.

When a vessel is docked or undergoing repairs, the main propulsion system may not be operational for extended periods. Without occasional movement, the propeller and shaft can suffer from undue stress or warping due to gravity and the weight of the propeller. By using the jacking gear, crew members can turn the shaft at low speed, which helps to evenly distribute wear, maintain the alignment of the propulsion system, and prevents any potential damage from static positioning.

Moreover, the jacking gear also allows for inspections and maintenance tasks that require the shaft to be rotated to gain better access to various components situated along its length, enhancing the overall maintenance process and ensuring the reliability of the propulsion system when it is returned to service.